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I'm making a couple of small modifications to a uClibC/busybox toolchain to make an OS to boot of a USB. I've installed GRUB onto it, and normally...
GRUB boots fine of the usb disk;
I run...
root (hd0,0)
kernel /boot/kernel root=/dev/sda1
boot
It boots the kernel, and gets as far as mounting the root file system, which fails.
This has happened to me many times before (I use LFS lol) and it's always been because of a missing fs driver, disk driver, etc. but i've checked twice and made sure that all the right drivers are compiled in.
I have a feeling that the trouble could be because my box has an inbuilt 4-in-1 card reader and these all show up as seperate usb devices.
Do i need something like an initrd to fix this up?

Is the file /etc/fstab pointing to the correct /dev/sd** and not a /dev/hd**?
4in1 card reader can be the issue unless the slot you are using is the on that will be designated as /dev/sda*. When normally booted up what /dev/sd** is the slot you are trying to use?

When i boot ubuntu (and LFS for that matter) it's /dev/sde
Im pretty sure it can't be /etc/fstab because that is on the root partition, which cant be mounted and therefore cannot be read.
I've tried all manner of root=/dev/sd* and none of them can be read. If i mount another root filesystem on /dev/hda* i can mount the usb as /dev/sde1 so im pretty sure all the drivers must be there...none of them are modules, what am i mising?

I had this same issue when I was trying to make a USB rescue disk. But some time back I fixed that problem.

I don't remeber what exactly the problem was but these are something that I have with the working copy.
1) Either compile SCSI & USB support statically or load it from InitRD (I don't need InitRD for everything else)
2) Figure out which bios drive GRUB is using for the USB drive (if the BIOS correctly loads the kernel from the USB drive thats may not be a problem. But may careful about root=/dev/xxxx).
3) May be you have to wait for some time (in the InitRD) until the '/dev/sdaxxxx' stuff comes up (after loading the SCSI & USB modules)

Right now I am using BusyBox & UDev with the USB Rescue disk.
Note: I am using a Debian Sarge stable & don't need InitRD for usual disk booting.